The present invention is a device used to generate a gaseous plasma in which an oscillating electromagnetic field ionizes neutral species in the gas phase to form ions and electrons, excites neutral species to form electronically excited atoms and molecules, and dissociates molecules to form atoms and radicals. Industrial plasma processing involves the exposure of a workpiece to the plasma effluents in order to remove material from the substrate surface (etching), grow material on the substrate surface (deposition), chemically alter the surface (plasma oxidation, nitration, surface cleaning and passivation), physically modify the surface (surface roughing or smoothing), or generally modify the conditions on the surface or in the body of the workpiece (e.g. plasma sterilization). The utility of a plasma source relates for many applications to the density of charged particles in the plasma, ions and electrons. This density, in turn, is governed by the rate of production versus the rate of loss of ions and electrons. Plasmas and plasma sources are characterized and differentiated not only by the density of charged particles in the resulting plasma but in addition by the frequency of the generating electromagnetic field and by the range of gas pressure or vacuum suitable for its operation. The following review of prior art is limited to the technology associated with plasmas generated by microwaves of frequency 2.45 GHz.